Up to now, many ideas have been proposed about load measurement of a time-varying force under dynamic states excited by shaking, oscillating and/or vibrating conditions. However, conventional load measurement methods and equipments are for measuring a static force or a quasidynamic force at measuring state conditions, over a long range period of about 1 second period, with a small acceleration depending on less than one G. Such conventional dynamic load measurements are not beyond a range of a static load measurement.
At first, conventional load sensors are described as a presupposition. A conventional load sensor is set up on a perfectly still base that and that a measuring load is constant and a time-independent force and that a measuring object is softly placed on the fixed measuring equipment, like a conventional scale.
In a conventional static load sensor, as shown in FIG. 1(A), the load measurement sensor assembly A is rigidly supported by a still fixed base B, and the measuring object C of the mass m is softly put on the sensor assembly A. This system forms a uniform motion coordinate, and the force F is given by the equation, F=mg (N=Kgm/s.sup.2), where g is a gravitational acceleration (m/s.sup.2). The static load S/L is time-constant and is independent of the measuring time, shown in FIG. 1(B). In FIG. 1(C) the acceleration A/L of the sensor assembly A is zero at all times.
Considering the case where the spring-mass load measurement equipment in FIG. 1(A) is subjected to a suddenly applied constant force, the sensor assembly A is set to vibrating by the suddenly applied dynamic force, such as by dropping the load measurement object C from an upper side to the sensor assembly A. The vibration and acceleration, whose plot against time is shown in FIGS. 2(A) and (B) is excited at a free edge of the sensor assembly A on the beam. The vibration of the free edge is attenuated by damping forces by the material and the structure of the beam that is composed for sensor assembly A. The damping forces extinguish the vibration in time. At last the external force is time-constant. In this condition the time-constant load can be measured. The same analogy is true for measuring a weight of human by a conventional scale.
Considering the case that the load measurement equipment in FIG. 1(A) is acted by a suddenly applied impulsive load that is excited by a moving object such as an automobile passing over the sensor assembly A, the time acted upon by an impulsive load is so short that the vibration and acceleration remain at the sensor assembly A. Since the vibration and acceleration of the sensor assembly A eventually die out in time and decrease to zero as shown in FIGS. 3(A) and (B), it is impossible to measure the load of the object.
Considering the case of the load measurement that the base B in FIG. 1(A) is subjected to a time-varying displacement, the load sensor in FIG. 1(A) is set up at a time-varying base B that is excited by external vibrating and oscillating forces as shown in FIG. 4(A). The measuring object C of the mass m is softly put on the sensor assembly A. This system forms a non-uniform motion coordinate. Since the displacement of base B' is time-varying, the measuring load is not constant. The acceleration G/L of the base B' in FIG. 4(B) is produced by external time-varying forces. The sensor assembly A is vibrated by an acceleration G/L of the base B' and an acceleration A/L of the sensor assembly A. Further the acceleration A/L excited by vibrations of the sensor assembly A is plotted by a solid line, and the acceleration G/L of the base B' is plotted by a break line.
Considering the case of the load measurement that the base B' in FIG. 4(A) is subjected to a time-varying displacement and that the sensor assembly A is acted on by a suddenly applied step and constant force, the load sensor assembly A in FIG. 4(A) is vibrated both by a time-varying base B' that is excited by external vibrating and oscillating forces and by a suddenly applied step force. Since the suddenly applied step vibration of the sensor assembly A eventually die out in time and decrease to zero by a damping effect. However the vibration by a time-varying base B' remains during action by an external force. As a result, it is impossible to measure exactly the load of the object as shown in FIG. 5(A). The acceleration of the sensor assembly B' is only excited by the external time-varying vibration. It is impossible to measure the load by only the acceleration of the object. The acceleration A/L excited by vibrations of the sensor assembly A is plotted by a solid line, and the acceleration G/L of the base B' is plotted by a break line as shown FIG. 5(B).
Considering the case of the load measurement that the base B' in FIG. 4(A) is subjected to a time-varying displacement and that the sensor assembly A is acted on by a suddenly applied impulsive force, the load sensor assembly A in FIG. 4(A) is vibrated both by a time-varying base B' that is excited by external vibrating and oscillating forces and by a suddenly applied impulsive force. In this case, the time acted upon by an impulsive load is so short that the vibration and acceleration of the sensor assembly A by the impulsive force eventually die out in time and decrease to zero as shown in FIG. 4(A). The vibration by a time-varying base B' remains during action by an external force. As a result, it is impossible to measure exactly the load of the object as shown in FIG. 4(A). The acceleration of the sensor assembly B' is only excited by the external time-varying vibration as shown in FIG. 6(A). It is impossible to measure the load by only the acceleration of the object. The acceleration A/L excited by vibrations or the sensor assembly A is plotted by a solid line, and the acceleration G/L of the base B' is plotted by a break line as shown in FIG. 6(A).